Rotary drill bits are customarily provided with a plurality of cutting edges disposed symmetrically about the axis of rotation of the bit. The torque required to turn the bit during drilling is the torque required for each cutting edge multiplied by the number of cutting edges. When drilling or enlarging holes in hard materials such as steel or iron, a high torque is required. This may result in overloading the motor by which the drill is driven.
It has also been proposed to provide a bit with a single cutting edge and an opposite rubbing surface for balancing the radial force on the cutting edge. However, the friction of the rubbing surface generates heat and represents a waste of energy.
It has been proposed to notch the cutting edges of drill bits, spade drills, counter bores, reamers, countersinks and the like to break up chip lengths and thereby aid in the removal of the chips particularly from deep machine-drilled holes. However, these notches have always represented a small percentage of the cutting edges and do not materially reduce the torque required to drive the drill bit.